1. Field of the Invention
This invention relates to acrylates in which a large percentage of hydrogen atoms have been replaced by halogens and to polymers that include mer units derived from such halogenated acrylates.
2. Background of the Invention
Optically transparent polymers, especially those used for telecommunication applications, must have low absorptive loss in the infrared wavelengths, typically 1260-1360 nm and 1480-1580 nm. However, because these wavelengths are close to overtones of carbon-hydrogen bond vibration frequencies, minimization of the number of carbon-hydrogen bonds is desirable. While some organic compounds with few C--H bonds are known, additional considerations of optical transparency, ease of polymerization, refractive index, chemical and mechanical stability, and the need to compete on a cost basis with glass prevent many such compounds from widespread use in polymeric optical devices.
U.S. Pat. Nos. 3,668,233, 3,981,928, and 4,010,212 describe acrylic acid esters (i.e., acrylates), prepared from esterification of acrylic acid with perfluoro-tertiary alkyl alcohols such as perfluoro-t-butyl alcohol, that can be used as inert heat exchange fluids and as homopolymeric water- and/or oil-repellent surface coatings.
European Patent Application No. 282,019 describes highly fluorinated, transparent acrylates specifically tailored for optical articles. These materials are prepared from cyclic or bicyclic alcohols containing few or no carbon-hydrogen bonds.
U.S. Pat. No. 3,544,535 describes the preparation and polymerization of 2-(pentafluorophenyl)hexafluoroisopropyl acrylate. Optical properties of the polymer are not described.
U.S. Pat. Nos. 3,520,863 and 3,723,507 describe a number of perfluorocycloalkyl acrylates and polymers thereof Use of tertiary alcohols is not reported, and optical properties of the polymers are not discussed.
U.S. Pat. No. 5,045,397 describes the preparation and use of certain adhesives to be used in optical systems. A polymeric adhesive of a specified refractive index is prepared by copolymerization of specified monomers of known refractive indices. While some lightly fluorinated monomers are described, highly fluorinated monomers are not disclosed.
U.S. Pat. No. 5,223,593 describes acrylate monomers and their (co)polymers designed to have low C--H bond density relative to poly(methylmethacrylate) so as to reduce vibrational band intensities in plastic optical fiber cores. Absorbance at 600-1200 nm was reduced, but absorbance at higher frequencies is not reported. The described acrylates were prepared from highly fluorinated primary alcohols.
U.S. Pat. No. 5,093,888 describes a polymeric optical device (specifically, an injection-molded Y-shaped splitter waveguide) that uses an amorphous polymeric adhesive that includes 2,2,2-trifluoroethyl methacrylate having a refractive index of 1.418 to hold optical fibers in a polytetrafluoro-ethylene spacer containing a fluorinated polyetheretherketone core.
U.S. Pat. No. 5,311,604 describes a method of manufacturing a polymeric optical interconnect. Useful polymers are said to be those transparent to the wavelength of light to be utilized. Listed examples include poly(methylmethacrylate) ("PMMA"), polycarbonates, polyurethanes, polystyrenes, and polyolefins. In one example, a "copolymer of deuterated PMMA-d8 (sic) and tetrafluoropropyl methacrylate" is used to adhere optical fibers to a molded PMMA device.
U.S. Pat. No. 5,343,544 describes a polymeric optical interconnect. The device includes polymeric substrate and covering members that can be fabricated from, for example, a combination of fluorinated and non-fluorinated photopolymerizable (meth)acrylate and di(meth)acrylate monomers. The same combination of monomers is said to be useful for sealing optical fibers in the device. Substitution of fluorines for hydrogen atoms in the polymer is said to be capable of reducing the refractive index of the polymer and to reduce losses in near infrared wavelengths, but no example of a haloacrylate-only system and no indication of the degree to which loss or refractive index can be controlled are given. Copolymerization of two or more monomers is said to be able to provide a copolymer having a tailored refractive index.
Devices used in telecommunication applications (such as those described in '604 and '544, above) preferably meet certain standards for performance, durability, and the like. The standards most commonly referred to in discussing such devices are the so-called "Bellcore Specifications". Requirements for fiber optic branching components include parameters for optical loss (i.e., loss that is in excess over that which is inherent in the device), useable wavelength ranges, resistance to performance variability caused by temperature and humidity, optical cross talk, water immersion, flammability, etc. All such parameters can depend, at least in part, on the materials used to make the device. For example, materials must have very low absorptive losses in the wavelength regions of 1260 to 1360 nm (nominally 1310 nm) and from 1480 to 1580 nm (nominally 1550 nm), over which ranges low losses must be maintained under extreme temperature and humidity conditions. For a 1.times.2 splitter, the inherent loss is calculated to be 3.01 decibels (dB), where a decibel is defined as -10 log(I.sub.o /I.sub.i) in which I.sub.o is the intensity of the output and I is the intensity of the input. Maximum allowable excess loss in a 1.times.2 splitter is quantified as, e.g., no more than 0.25 dB per fiber plus no more than 0.5 dB per waveguide junction connecting an input fiber to an output fiber.
Presently available materials other than glass have not proven to be able to meet all, or even most, of these rigid requirements.